Processing is using a Java2D mode so the underlying Processing object
used is a PGraphicsJava2D
object.

This render target supports two modes: applet or headless. The
applet mode is what is used in Gephi GUI and is backed by a PApplet
with zoom and pan control. The headless mode is tuned to work without GUI and
is typically used in exports. Either way users should use getGraphics()
method for drawing.